1. Field of the Invention
The present invention relates to a method for forming a pattern.
2. Discussion of the Background
In manufacturing integrated circuit elements and the like, a method for forming a pattern utilizing a multilayer resist process has been in widespread use to meet miniaturization of processing size. In the multilayer resist process, a resist underlayer film is generally formed by coating on the upper face side of the substrate to be processed with a composition for forming a resist underlayer film, and a resist coating film is formed by coating on the upper face side of the resist underlayer film with a resist composition. Then, a mask pattern is transferred to the resist coating film through the irradiation of radioactive ray by means of a stepping projection aligner (stepper) or the like, and subsequent development with a proper developer solution gives a resist pattern. Subsequently, the resist pattern is transferred to the resist underlayer film by etching. Finally, the resist underlayer film pattern is transferred to the substrate to be processed by etching, whereby the substrate with a desired pattern can be obtained. Furthermore, a multilayer resist process involving three or more layers may be employed, in which an intermediate layer is further provided on the upper face side of the resist underlayer film. Additionally, in the formation of the resist pattern other methods that exclude the use of the resist composition, for example a nanoinprint method, are also used.
Generally, materials having a high carbon content are used for the resist underlayer film placed directly on the substrate to be processed. Such a high carbon content leads to the increase in etching selectivity at the time of the processing of the substrate to be processed, which enables more precise pattern transfer. Thermosetting phenol novolak resins are particularly well-known as materials for the underlayer film. Additionally, it is known that a composition containing an acenaphthylene based polymer exhibits favorable characteristics as the underlayer film (see Japanese Unexamined Patent Application, Publication Nos. 2000-143937 and 2001-40293).
Since the above-described resist underlayer film becomes useless after the pattern formation by the etching, it is removed by ashing or the like. The ashing is typically a process in which oxygen plasma is generated and organic components in the resist underlayer film are burned out by oxygen radicals in the plasma. A technique for peeling the resist underlayer film with a solution has been proposed (see Japanese Unexamined Patent Application, Publication No. 2004-177668).